Several packages and packaging techniques for encapsulating integrated circuits are known in the art, such as glass, metal, ceramic and plastic packages.
As electronic products increase in functionality and complexity, there is an emphasis on affordability, miniaturization, and energy efficiency of the semiconductor devices as a whole. The telecommunications, automotive, and commercial electronic markets are the leading drivers for these trends. These markets see high volume manufacturing with millions of units on a yearly basis. The choice of the packaging material for the electrical components for these markets can have a substantial impact on the cost of the final product. Therefore plastic encapsulate components are almost universally used in non-military applications over the conventional ceramic or metal electronic packages. Metal and ceramic packages are mostly used when hermetic packages are required, such as in military applications.
Plastic packaging may use organic materials for environmental protection. In contrast to hermetically sealed packages, organic material usually contacts the active element (or a thin inorganic barrier layer) in the plastic package.
Post molded and pre-molded plastic packaging is the dominant technology in packaging today. Post molded plastic packages are formed after chips are attached to the mounting surface, such as a metal lead frame, and are electrically connected. Typically, a thermosetting epoxy resin is used to form the package body around the chip and mounting surface. There are many types of post molded packages due to the popularity and versatility of polymers. However, this process does subject the die and wire bonds of the package to the harsh molding environment.
Pre-molded packaging provides a less harsh environment for packaging sensitive chips requiring a low cost assembly. The main element is that the chip and interconnects are decoupled from the molding process. The package is made by either a transfer molded process using a thermosetting epoxy resin or an injection molding process. The chip and interconnects are then encapsulated to protect them from the environment. In some cases, a plastic lid is used to seal the plastic package. The ejection molding process easily produces cavity style packages that are increasingly useful for newer optical and electromechanical chips (MEMS). The injection molding process allows for precise cavity packages to be manufactured automatically.
EP0813236(A1) describes a method of encapsulating an integrated semi-conductor circuit, by bringing a column into contact with the integrated circuit before applying a molding compound, so as to form a cavity on top of the integrated circuit when the column is removed. A tube was also used before applying the molding compound so as to create an edge for fixing a window component can be fitted to close the cavity.
US2002/0168795(A1) describes a method for encapsulating a pressure sensor into a package, whereby a mold comprising a pin is used to create an opening in the package. After removal of the pin, an airway is created to the pressure sensor.
FIG. 1(a) to FIG. 1(c) are schematic representations of a process that can be used for encapsulating an integrated circuit that is sandwiched between a substrate (bottom) and a transparent cap layer (top). The mold has a protrusion which is brought into contact with the cap layer for defining an opening to be made in the package for allowing passage of radiation, e.g. light.